well im not really sure, but he got the non-XT model (weighs less) but he literally cut off the pipe and welded one on that he modded himself (idk about any details), he had these huge 28 inch mud tires, compared to the 25 inch tires that he said the speedometer was calibrated to, and the speedometer was between like 75 and 82 or so when i had it cranked out, and since i live in a mountainous area all of the roads i was on were mostly downhill so it was somewhere around the 80-90mph range, but not over 90.. it tended to jump between 4 and 10 mph when i went down steeper hills compared to straight-aways and uphills

it was crazy, i wasn't wearing goggles and the helmet caught some pretty good pressure to a point where its really hard to breathe, it feels like you're flying.. i jerked my head back once to adjust the helmet and i didn't have a strap on so the helmet ripped off my head and i had to turn around to get it off the side of the road.. its crazy, if you know anyone who has one then you definitely have to try it out (full throttle the whole time otherwise its pointless)

 

I own both a 400EX quad and an XR400 motorcycle. Motors are nearly identical except for electric start only on 400EX and kick start only on XR400. I believe these are most reliable middle weight dirt motors of all time. My grandkids started riding my 400EX at age 14 after many years on motorcycles and do really well on it. Plenty of power in the dunes and still very manageable on tight trails. Most experienced riders will also confirm that the 400EX is the best quad of all time for learning tricks like wheelies, jumps, and stoppies.

 

80-90? on 28" mud tires? on pavement? no helmet? 50 miles?

one-sounds like a good way to die...
two-that fast on pavement with a high cg, short wheelbase, narrow track, narrow tire with that much sidewall sounds like its very very unstable even way before youre hitting 80.


but if you like doing that then get the 450. I ride a 400 ex, its got the hot rods 460 stroker kit, PP head, hot cams stg 2 cam, fmf powerbomb head pipe, fmf can, kn filter, jetted, and I would like more power. and if its too powerful that its no fun then gear it up and then there you go, less launching power and more top-end.

and my girls got a piped/jetted 04YFZ down one in front and their performance is very similar. still searching for the correct gears on the 460 though, likeing the current 15/36 but never rode with her on them yet. and the 06 YFZ was supposedly more powerful than the 04YFZ, the 06 honda more so than that and the 07 honda more so than the 06.

and shes had the YFZ for over a year and oh wow you change the oil/filter, adjust the valves rarely, new plug now and then, clean the air filter, and it still runs like new. these are things I would be doing to my 250ex if I bought one new, to anything I spent thousands on come to think of it, so when I buy mine it will require no more maintance than any 4 stroke toy ive ever owned.